Bacteria become resistant to antibiotics when stressed, finds research published in BioMed Central's open access journal BMC Evolutionary Biology. In particular E. coli grown at high temperatures become resistant to rifampicin. It is generally thought that antibiotic resistance is costly to maintain, for example mutations which reduce antibiotic uptake also restrict the amount of nutrients entering the cell. Consequently in the absence of antibiotics non-resistant bacteria will out-compete the resistant ones. However researchers from UC Irvine and Faculté de Médicine Denis Diderot have discovered that by putting bacteria under stress, by growing them at a high temperature, the bacteria could spontaneously develop resistance to the antibiotic rifampicin.